The present invention relates to a mathematically definable outline character font and character generating system having particular, but not necessarily exclusive, application in electronic printing and/or visual displays.
Until recently, the bulk of typesetting was accomplished using photo-mechanical means. Typically performed on photo-compositors, this method of generating type is generally limited to 24 words per hour since each typeset character involves exposure through a film strip onto an underlying sheet of photosensitive paper. Once text has been fully exposed onto the photographic paper, the paper is then developed and subsequently positioned and affixed to a layout page. After layout is complete the page is then rephotographed with the resulting negative being retouched prior to creating an offset plate for printing to remove unwanted lines and marks that often appear on the negative.
The mechanics of typesetting and layout are undergoing significant changes. While photo-mechanical approaches are still being employed by many to typeset, their use is rapidly being replaced by a newer, electronic imagesetting technology. Faster and less expensive computers, and their associated input and storage devices and the availability of more sophisticated type generating software has brought the ability to produce high-resolution documents within the reach of more users than previously possible. Electronic layout, which enables a layout artist to electronically manipulate digitized images and text on a video display screen prior to printing it, eliminates the bulk of the mechanical layout effort. Using electronic layout techniques, a final layout may be output directly to a laser printer or to a high-resolution photographic imagesetting device without the need for the intermediate paste-up and photographic steps. Yet, however convenient electronic typesetting may be, it is viable as an alternative to other typesetting methods only if the perceivable typographic quality is comparable to that previously rendered by the slower photo-mechanical technique.
Several methods are available for electronically encoding a typeface including storing characters as bit maps and storing as mathematical descriptions of the characters' outlines. Since outline fonts are generally output device independent and offer a greater degree of resolution, they are the preferred choice for imagesetting applications. Currently the most widely accepted method for describing outline character fonts is a page description language called PostScript.RTM. by Adobe Systems. PostScript provides a means for describing and storing the graphical attributes of individual typeface characters mathematically as a combination of arcs, lines, curves and control points. Once defined, each character may be assigned a unique identifying number (0-255) conforming to a location in an ASCII character table for subsequent retrieval by an input device. Since outline characters are precisely described as a combination of mathematical elements, proportional sealing or digital manipulation may be performed without loss of the character's mathematically described features. In the above regard, reference is made to the following technical publication: "PostScript Language Reference Manual", Adobe Systems, Incorporated, Addison-Wesley Publishing Co., Inc. 1986.
Subsequent to being retrieved from their character table, a character outline may be filled to provide a solid font character for printing. Once the characters are filled they are prepared for printing using a rasterizing technique. Rasterizing produces a stream of data that when sent to a printer, such as a laser printer or imagesetter, yields a filled representation of the character outline stored in the font character table. Because of their mathematical nature, outline fonts may be sent to any output device equipped with suitable language interpreter, their resolution being limited only by the physical limitations of the rastering device.
As a result of the increased demand for electronic typesetting, literally thousands of outline fonts have been either created or derived from existing, mechanical typefaces using digitizing devices and outline font generating software available in the art, such as Fontographer.RTM. by Altsys. Font generating software converts hand sketched or traced character images into mathematical PostScript descriptions of the characters' outlines. After a complete set of characters in a typeface is converted, the collection is assigned a unique PostScript font identification number. When creating an electronic font, the spatial relationship, between adjacent characters may be just as critical as the description of the character itself. To accommodate situations where a character may change depending upon the context of its use, i.e., its context-sensitivity, electronic fonts may provide kerned pairs, ligatures, and composite character elements, such as accents. While not generally visible on a standard ASCII keyboard, these special characters are generally invokable by their ASCII address entered through a sequence of keystrokes on a keyboard.
A truly context-sensitive cursive typeface converted to an outline font will produce some characters with more than one outline description. For example, a context-sensitive, lower case "e" will appear in numerous forms depending upon its placement within a word and with which adjacent character it is connected. An e at the beginning of a word may differ form an e falling at the end of a word. So too, an e following a b has a differently shaped bowl and connecting point than an e that connectingly succeeds an l. Compounding the problem is the fact that both cases of a typeface, i.e., 52 alphabetic letters plus special, accented forms, must be considered. Consequently, if an outline character was generated for each possible permutation of a character based upon its contextual relationship, the font character table would soon become unmanageable by quickly exceeding the total of 256, the maximum number of characters available in a single font character table and addressable from a standard ASCII keyboard.
Examination of the art of mechanical typesetting discloses a plethora of typefaces with the two basic typeface families being manuscript and cursive. Cursive, sometimes referred to as script, is usually intended to emulate human handwriting. As such, a cursive type style relies heavily on context-sensitive characters, that is, character letter forms that change depending upon the characters with which they are joined. This is especially true with the Zaner-Bloser typeface which has, since the late 1800's, been used to instruct pupils in Zanerian method of correct cursive penmanship by creating exemplars for pupils to mimic. This familiar typeface uses a series of interconnected flowing strokes and curves to produce a pleasing handwriting display while accommodating the limited motor skills of the beginning cursive handwriting student.
Since the number of character variations required to produce a context-sensitive cursive type style exceeds the standard ASCII character set of 256, past efforts to create a context-sensitive outline font have relied on the creation of numerous, related fonts, each containing only a portion of the entire cursive character set. In setting context-sensitive type, appropriate characters would have to be selected from several different fonts depending upon its typographical environment. Therefore, to set cursive type using a PostScript outline fonts, more than one font had to be downloaded to the PostScript printing device for a given block of text. In addition to being awkward to implement, the use of multiple outline fonts to represent a single character set is both time consuming and an inefficient use of memory in the PostScript printing device which generally stores bitmapped renditions of the downloaded fonts in the printer's memory.
It is the generation of a context-sensitive cursive outline font which may be stored in a single standard ASCII character table to which the present invention is addressed.